High speed spark discharge print device



June 1965 B. J. GREENBLOTT ETAL 3,137,669

HIGH SPEED SPARK DISCHARGE PRINT DEVICE Filed Dec. 24, 1962 FIG.

FIG. 2

INVENTORS BERNARD J. GREENBLOTT ROBERT J. HART A770 IVE) United States Patent 3,187,669 HIGH SPEED SPARK BiS'iCHAR-GE IRZNT DEVEQE Bernard J. Greenhiott, Needham, Mass, and Robert 3'. Hart, Johnson City, NFL, assignors to International Business Machines Corporation, New York, NE a corporation of New York Filed Dec. 24, 1962, Ser. No. 246,721 4 Claims. (Ci. 1191-114) This invention relates to high speed printing and more particularly to an improved printer device which utilizes shock wave and plasma energy from a spark discharge in a compressible gas.

Printing devices and methods are known in which pressure waves produced in a compressible gas are used to perform a work function which produces a mark on a record medium. Heretofore, such prior devices and methods required the movement of a type element or marking member or extensive movement of a paper against such an element or member to produce an imprint. Because of the extra mass involved in such mechanisms and methods of printing, high energy was required thereby reducing the efiiciency of printing, the speed of impacting was somewhat limited, and the repetition rate whereby successive imprints can be accomplished wasalso limited. The net effect of such limitations was therefore to reduce the speed potential whereby large quantities of data can be printed.

It is the general object of the present invention to provide an improved spark discharge printing device in which the above defects andlimi'tations are avoided.

It is a specific object of the present invention to provide an improved spark discharge printing device which utilizes shock wave and plasma to obtain greater print efficiency, impacting speed, and an improved repetition rate of impact with less consumptionof energy to afford a potentially higher print output.

It is a further object to provide an improved printing device in accordance with the previous objects which would also provide good quality printing at high speed.

A still further object of the present invention is to provide an improved printing device whereby higher printing speeds are obtainable with improved efficiency without sacrificing print quality.

The above as well asother objects are attainable in accordance with thepractice of the present invention by producing a pattern of shock waves and plasma in a compressible gas in the form of a character to be reproduced and impacting a pressure sensitive record material directly with the pattern of waves and plasma to produce a visible mark having the desired data identification. Thus, the method eliminates the mass of an impact element or the mass of a paper to be moved thereby increas ing the efficiency of printing. In the preferred form, the data pattern is produced by shaping shock waves and plasma generated in a compressible volume of gas by a spark discharge. By utilizing shock wave and plasma generated by the spark discharge in a compressible gas, a high impact speed is attainable since shock wave and plasma phenomena travel in gas, such as air at ambient pressure and temperature, in the supersonic velocities. In the preferred embodiment, the shock wave and plasma generated in a finite volume of gas are passed through a stencil member having apertures arranged to shape the shock waves and plasma in the form of data to be printed. The shaped waves and plasma are then directed against a pressure sensitive marking medium which might preferably include one or more sheets of interleaved paper and carbon paper.

In the preferred embodiment of the invention, the spark discharge printer device comprises a shock wave and plasma generator including electrodes mounted on a shock wave reflector member. The electrodes are mounted on I the reflector member in a manner such that a spark gap is way is positioned adjacent the reflector member so that the passageway defines a finite volume of gas with the reflector member in the region of the spark gap. A stencil member having shock wave and plasma shaping aperture means therethrough is positioned against the focusing member such that the aperture means overlay the end of the focusing passageway. In the preferred form the shaping apertures through the stencil member are tapered so that one or more converging channels is provided for the shock wave and plasma produced in the compressible gas within the focusing passageway. Improved print quality has been obtained at high speeds utilizing such tapered apertures in the stencil member. In the preferred embodiment both the focusing channel and the stencil apertures are tapered so as to present successive converging passageways from the reflector member to the region of impact with a print medium. However, the desired improved print quality can be realized with focusing passageways which are either straight or diverging when used in combination with the convcrgingly tapered apertures through the stencil member. In such a device, high speed impacting is readily attainable because neither marking element nor print medium need be moved against an impression device to form the imprint. A h-igherrepetition rate within the limitations of the energizing means for producing a spark discharge from the electrodes becomes possible. Furthermore, a higher impact and repetition rate necessarily affords greater output print speed.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a section drawing with circuit diagram showing the spark discharge print device of the subject invention.

FIG. 2 is a plan view of a stencil member of FIG. 1 illustrating the single alphabetic character U.

FIG. 3 is a perspective view showing the spark generator assembly of FIG. 1.

FIG. 4 is a pictorial representationillustrating the operational steps for practicing the method of the present invention.

FIG. 5 is a perspective view in schematic of a high speed printer apparatus embodying spark discharge print devices in accordance with the present invention.

Referring to the drawings in FIG. 1, an assembly for printing with a pattern of shock waves and plasma comprises an electrode support and shock wave reflector plate 10 which may be mounted on a support plate 11 by suitable means such as brackets 12 and screws 13. In the preferred embodiment, reflector plate 13 is a block formed of electrical insulating mate-rial preferably a moldable plastic. A pair of electrodes 14 and 15 are mounted on plate 10 for generating a spark discharge adjacent the upper face ltia thereof. The electrodes 14 and 15 are mounted on the plate 10 in such a manner that a spark gap 16 is formed between the ends thereof across the face Ida of plate It While various techniques may be used for mounting the electrodes onplate 10, in the preferred embodiment, the electrodes 14 and 15 are conductor strips of material such as tungsten embedded in block 10 so that the conductors lie in the surface 10a of block 10 on either side of the gap 16.

Means for producing a spark discharge across gap 16 of electrodes 14 and 15 comprises a storage capacitor 17 connected in series with a firing switch by leads 19 and Ii 24 to electrode 14 and to electrode 15 by lead 21. When capacitor 17 has been energized to the appropriate energy level, switch 18 is closed to apply a potential adequate to produce breakdown across gap 16 in the gas adjacent the gap 16 thereby generating shock waves and plasma which are reflected by surface 1011. I

Various means may be provided to charge capacitor 17 as is known in the art. One form shown in FIG. 1 includes an electrical power source such as battery 22 connected by leads 23 and 24 in series with charging switch 25 to one side of capacitor 17 and'by lead to the other side thereof, With firing switch 18 open, on the closing of charging switch 25, battery 22 is connected across the capacitor 17 causing it to become charged to an energy level to produce a spark upon discharge. Upon comple tion of the charging operation, charging switch 25 is opened. The operation of switching means to perform the charging and discharging of capacitor may, of course, be performed manually or automatically using control elements well known in the art.

For the purposes of practicing this invention, capacitor 17 is preferably an energy storage capacitor having a low internal inductance, internal resistance. An energy storage capacitor of approximately 0.5 microfarad was found desirable for producing -7 kv. discharges across gap M having a Width of .O3(),.15() inch.

In accordance with the present invention, the spark discharge occurs in a finite volume of a compressible gas at an energy levelwhich produces shock wave pressure disturbance with plasma which. is shaped into a data pattern of shock waves and plasma and then directed against a pressure sensitive print medium. As seen in FIGS. 13, the preferred device for accomplishing this includes a focusing plate member or cap 3i having a focusing passageway 31 therethrough. The focusing plate 3% which preferably is formed of a molded plastic material with the passageway 31 machined therethrough is positioned to rest on and coact with surface lltla of reflector plate 19 with the passageway 31 located to define a ga filled region proximate spark gap 16. One suitable material usable for making the focusing plate can be an acrylic resin such as methyl rnethacrylate which is commercially available, for example, under the trademark Lucite.

To shape the shock wave and plasma a stencil plate member 32 having wave and plasma shaping apertures 33 configured to define a data pattern is superimposed on the focusing plate 36 to place the wave shaping apertures I 33 in alignment with the upper end of the passageway 31. Stencil member is preferably made of metal such as brass and the apertures are ground therein by a power tool or the like. A pressure sensitive medium, preferably comprising a paper sheet 35 superimposed on a pressure sensitive ink bearing paper 36 is placed to overlay the apertures 33 in stencil member 32. A flat surfaced backup plate 37 overlays the print medium 34. The entire assembly is secured and the position of the stencil member 32, focusing plate 30 and reflector plate 10 is maintained by means such as screws 38 which pass through suitable openings in the various members into threaded engagement with openings 10b in reflector plate Jlti (see FIG. 3).

While various types of focusing passageways 31 and wave shaping apertures 33 may be formed in focusing plate 30 and stencil member 32 respectively, in the preferred form, both passageway 31 and apertures 33 are tapered as seen in FIGS. 1 and 2. In addition, improved printing results with the focusing plate 3t) and stencil member 32 arranged so that the large ends of the openings face the reflector plate 10 so as to present a succession of converging channels downstream from the spark gap 16.

FIG. 4 illustrates pictorially essentially what occurs in practicing the present invention. With the focusing plate 30 in position against reflector plate 10, and stencil plate 32, print medium 34., and backup plate 37 superimposed in that order, a spark discharge at one end of passageway 31 sets up a shock wave disturbance id and generates plasma in the gas or air Within passageway 31. The shock wave 453 and plasma are reflected from reflector surface El c a of reflector plate 16 and emanate from passagewayfil to impinge on the inner face of stencil member 32. Portions of the shock wave and plasma pass through the apertures 33 thereby taking on the pattern characteristic of the apertures as identified by wave lines 41 and 42. The wave and plasma pattern'so produced are thus directed by the stencil member 32 against the print medium 34 where an impact occurs. The backup plate 37 being completely fiat, the visible imprint resulting is entirely attributable to the wave and plasma pattern produced by the stencil.

While FIG. 4 shows the parts widely separated, in actual practice, they are preferably assembled in close proximity more or less in the manner shown in FIG. 1. The separation of FIG. 4 was made for purposes of illustrating the wave and plasma generation and shaping in a pictorial'manner. In addition, it is to be noticed that in FIG. 4, the heavy lines, e.g., 43, represent successive peaks in the shock waves, a phenomenon associated with a spark discharge using an underdamped capacitor discharge circuit as shown in FIG. 1.

FIG. 5 illustrates a printer apparatus embodying the principles of the present invention in a form which produces printing of data a line at a time. A pressure sensitive print medium of the type shown in FIG. 1 takes the form of a continuous document 50. Behind document 5th is a backup plate or platen 51 and on the other side is a shock wave impact generator assembly 52 comprising plural spark generators uniformly spaced apart and arranged in a row along a print line. At each print position there is a spark generator comprising a pair of electrodes '53 and 54 with focusing plate member 55 having a focusing passageway 56 formed therein. in the embodiment shown in FIG. 5, the shock wave shaping means is a stencil member taking the form'of a continuous band 57 having a plurality of character apertures 58 and mounted on a pair of spaced drive pulleys 59 and 6f the former being connected to a drive means 61. With drive means 61 operating, the stencil band 57 moves at a continuous rate of travel past the various passageways 56 in the focusing plate 55. Upon the arrival of various character configurations 58 in the stencil band 57 at the various print positions, the various electrodes 53 and 54 are energized to. generate shock Waves and plasma within the individual passageways 56 which are shaped at the appropriate print positions by character apertures 58 causing the various select wave patterns to impact print medium 5t? against platen 51. When a line of data has been printed, document 5% may be moved in a manner Well known in the art to a second'line position and the oper ation repeated- While the invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. A spark discharge impact printing device compris- 0 ing in combination (a) a spark generator including electrode means mounted on a reflector member,

(b) said electrode means being mounted on said reflector member such that a spark gap is formed by said electrodes adjacent a surface of said reflector member, i i

(c) means for producing a high energy spark discharge across said electrode means pressure wave reflector member, v

(d) focusing means positionable adjacent said surface of said reflector member, said focusing means having a focusing passageway positionable at one end against said reflector surface so as to define a finite volume of a compressible gas in the region proximate said spark gap,

(e) a stencil member having shock wave and plasma shaping apertures therein operable for producing a data pattern of shock waves and plasma from shock waves and plasma produced in said gas Volume in said focusing passageway,

(f) means for locating said stencil member with said shaping apertures adjacent the second opening of said focusing passageway,

(g) and platen means for supporting pressure sensitive record material adjacent the anterior surface of said stencil member in impact receiving position over said shaping apertures in said stencil member.

2. A spark discharge printing device in accordance with claim 1 in which (a) said focusing passageway is convergingly tapered from the opening adjacent said reflector member to said stencil member and said stencil member is positioned adjacent the lesser opening of said tapered passageway.

3. A spark discharge printing device in accordance with claim 1 in which (a) said shock wave and plasma shaping apertures of said stencil member are convergingly tapered and said stencil member is positioned adjacent said focusing plate so as to present converging passageway to said shock Wave and plasma emanating from said focusing passageway.

4. A spark discharge printing device in accordance with claim 2 in which (a) said shock wave and plasma shaping apertures of said stencil member are convergingly tapered and said stencil member is positioned adjacent said focusing plate so as to present converging passageway to said shock Wave and plasma emanating from said focusing passageway.

References Cited by the Examiner UNITED STATES PATENTS 1,795,564 3/31 Korge 1011 X 2,405,714 8/46 Ryan 1014 X 2,467,034 4/49 Hutt 1014 X 2,604,042 7/52 Cool; 101-4012 2,737,882 3/56 Early et a1. 101-109 X 3,015,263 1/62 Lounsberry et a1. 101-109 X WILLIAM B. PENN, Primary Examiner. 

1. A SPARK DISCHARGE IMPACT PRINTING DEVICE COMPRISING IN COMBINATION (A) A SPARK GENERATOR INCLUDING ELECTRODE MEANS MOUNTED ON A REFLECTOR MEMBER, (B) SAID ELECTRODE MEANS BEING MOUNTED ON SAID REFLECTED MEMBER SUCH THAT A SPARK GAP IS FORMED BY SAID ELECTRODES ADJACENT A SURFACE OF SAID REFLECTOR MEMBER, (C) MEANS FOR PRODUCING A HIGH ENERGY SPARK DISCHARGE ACROSS SAID ELECTRODE MEANS PRESSURE WAVE REFLECTOR MEMBER, (D) FOCUSING MEANS POSITIONABLE ADJACENT SAID SURFACE OF SAID REFLECTOR MEMBER, SAID FOCUSING MEANS HAVING A FOCUSING PASSAGEWAY POSITIONABLE AT ONE END AGAINST SAID REFLECTOR SURFACE SO AS TO DEFINE A FINITE VOLUME OF A COMPRESSIBLE GAS IN THE REGION PROXIMATE SAID SPARK GAP, (E) A STENCIL MEMBER HAVING SHOCK WAVE AND PLASMA SHAPING APERTURES THEREIN OPERABLE FOR PRODUCING A DATA PATTERN OF SHOCK WAVES AND PLASMA FROM SHOCK WAVES AND PLASMA PRODUCED IN SAID GAS VOLUME IN SAID FOCUSING PASSAGEWAY, (F) MEANS FOR LOCATING SAID STENCIL MEMBER WITH SAID SHAPING APERTURES ADJACENT THE SECOND OPENING OF SAID FOCUSING PASSAGEWAY, (G) AND PLATEN MEANS FOR SUPPORTING PRESSURE SENSITIVE RECORD MATERIAL ADJACENT THE ANTERIOR SURFACE OF SAID STENCIL MEMBER IN IMPACT RECEIVING POSITION OVER SAID SHAPING APERTURES IN SAID STENCIL MEMBER. 